"The evolution of complex life on other worlds is rare in frequency but large in absolute number," according to new research from a team led by Louis Irwin—from the Department of Biological Sciences, University of Texas at El Paso. Their findings are based on the first plausible "assessment of complex life in the Universe using empirical data."

The team developed Biological Complexity Index (BCI), designed to provide a quantitative estimate of the relative probability that complex, macro-organismic life forms could have emerged on other worlds. Their calculation in the Milky Way alone is mind-bending: 100 million worlds in our home galaxy may harbor complex alien life. And the Milky Way is one of some 500 billion galaxies in the Universe.

The BCI ranks planets and moons by basic, first-order characteristics detectable with available technology. By our calculation only 11 (~1.7%) of the extrasolar planets known to date have a BCI above that of Europa; but by extrapolation, the total of such planets could exceed 100 million in our galaxy alone. This is the first quantitative assessment of the plausibility of complex life throughout the universe based on empirical data. It supports the view that the evolution of complex life on other worlds is rare in frequency but large in absolute number.

Rational speculation about biological evolution on other worlds is one of the outstanding challenges in astrobiology. With the growing confirmation that multiplanetary systems abound in the universe, the prospect that life occurs redundantly throughout the cosmos is gaining widespread support. Given the enormous number of possible abodes for life likely to be discovered on an ongoing basis, the prospect that life could have evolved into complex, macro-organismic communities merits serious consideration.

The team says that only 11 of the more than 1,700 planets so far discovered in the Milky Way have a higher BCI than Jupiter's moon Europa.

Comments

If 100 million planets in the Milky Way harbor complex life, that explains the fact that our attempts to detect them via Radio and Visual telescope observation has been utterly fruitless.

I think that developing technologies that are similar to ours on any given complex life planet is pretty darn infrequent. Infrequent enough that if there's just 100 million planets that "do" complex life, the stats and reality is enough to separate us and them by a 500 light years AND 500,000 years.

It would seem reasonable that we just perhaps get a rare blip of something such as the WOW signal... But unless those telescope arrays win the lottery, or we get much more advanced in our observation technology, we might as well be alone.

Excuse my ignorance .. but surely the easiest way to check if a planet has intelligent life would be to check if their are lights at night similar to what earth looks like at night from above? or wont we be able to see this outside of their atmosphere?

See the later article on the moon and complex life. If that article is correct ,than the 100 million this group found is way, way too large. if you need just the right kind of moon to form complex life, Then the number falls to a few hundred thousand, perhaps lower based on other factors that we have yet to discover. The likelihood of our kind of intelligent life may be as small as a mere handful per galaxy

Why are we all thinking that for life to evolve in other planets the conditions needs to be like the conditions on earth - why cant life evolve where the alien breathes carbon dioxide and exhale oxygen eats mercury for dinner cos his anatomy allows him to get the best out of mercury.